1. Field of the Invention
The present invention relates to the evaluation of an N-dimensional basis function. More particularly, the present invention relates to a VLSI analog circuit which evaluates N-dimensional basis functions.
2. Art Background
Analog circuits which generate a correlation output to signal inputs are well known. For example, analog adders and multipliers generate an output based on input such as voltage or current. One such circuit is referred to as the "bump" circuit. Delbruck disclosed a bump circuit which computes generalized measures of similarity or dissimilarity of two voltage inputs. For example, if the circuit determines the similarity of two inputs, the similarity outputs from the circuits given as currents become large when the input voltages are close to each other. As such, it computes a basis function in a single dimension. An equation representative of the "bump" circuit is shown below. ##EQU1## For further information regarding sub-threshold and above-threshold circuits, see U.S. Pat. No. 5,099,156, "Sub-threshold MOS Circuits for Correlating Analog Input Voltages" and Delbruck, "Bump Circuits for Computing Similarity and Dissimilarity of Analog Voltages", California Institute of Technology Computation and Neural Systems Program, CNS Memo No. 10, May 23, 1991.
However, with increasing sophistication in the design of analog circuits for application in certain technology areas, such as neural networks, it is desirable to produce a circuit which implements a basis function in multiple dimensions.